The Economics of Reservoir Sedimentation: A Case Study of Mahaweli Reservoirs in Sri Lanka

Benefits of water resource projects often fall short of original expectations owing to sedimentation of reservoirs. This study estimates the cost of reservoir sedimentation in Mahaweli reservoirs including impact on hydropower production, irrigation water supply, extra cost of water purification and loss of fisheries yields. The present value of the cost of sedimentation is estimated to be US$26 406 620. Of the different types of costs, lost hydropower production is the most significant as it accounts for 66.6% of the total cost. The benefits of prevention of reservoir sedimentation alone are inadequate to compensate for the costs involved. Using soil erosion control measures at farm level offers a better solution for reservoir sedimentation compared with de-silting. Among the available erosion control methods, stoned terrace is the least-cost solution to reservoir sedimentation.